Method of changing the conductivity of ceramic materials



July 16, 1968 G. E. BLAIR ETAL METHOD OF CHANGING THE CONDUCTIVITY OFCERAMIC MATERIALS Original Filed March 18, 1963 2 Sheets-Sheet 1 z a Lwt as v; o Ba (PO,

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TEMPERATURE I/oK TEMPERATURE l/oK INVENTORS FIG. 2 mm DAVID P. HAMBLEIIROBE!!! A. WEIDEL ATTORKEYS July 16,

Original Filed March 18, 1963 OHM CM.

1968 G. E. BLAIR ETAL 3,393,060

METHOD OF CHANGING THE CONDUCTIVITY OF CERAMIC MATERIALS 2 Sheets-Shet 2Z 9 U) Q I (D Z :1 k-

IO I- a I I WAVE LENGTH- MICRONS o I; 3 0 0 0 11L zie aid TIME MINUTESINVENTORS GERALD E- BLAIR DAVID R BAMBI-EN ROBERT A. WEIDEL ATTORNE 8FIG. 4

United States Patent O 3,393,060 METHOD OF CHANGING THE CONDUCTIVITY OFCERAMIC MATERIALS Gerald E. Blair, Galita, Calif., and David P. Hamblen,Gates, and Robert A. Weidel, Webster, N.Y., assignors to Bausch 8: LombIncorporated, Rochester, N.Y., a corporation of New York Continuation ofapplication Ser. No. 265,636, Mar. 18, 1963. This application Oct. 13,1966, Ser. No. 586,573

2 Claims. (Cl. 65-33) ABSTRACT OF THE DISCLOSURE A method is disclosedfor reducing the specific resistivity of a glass composition includingthe major portion of vanadium pentoxide and a minor portion of numerousmetal phosphates. The glass substrate is heated in a temperature rangebetween the transition temperature and the liquidus temperature for aperiod of time sutficient to cause crystallization. The crystallizationeffectively reduces the specific resistivity of the glass.

This application is a continuation of Ser. No. 265,636, filed Mar. 18,1963, now abandoned.

This invention relates to a method of changing the conductivity ofceramic materials and more particularly to a method of treating vanadiumphosphate materials in order to change the electrical characteristicsthereof.

The increased interest in ceramic semi-conductors has led to severalstudies of the electrical properties of various ceramic compositions.Such studies have indicated that glass compositions which contain highpercentages of vanadium oxide produce glasses which have characteristiclow resistivities. Glasses of this type have been disclosed in theBritish Patents 744,205 and 744,947 which were published on Feb. 1,1956, and Feb. 15, 1956, respectively.

Attempts to utilize vanadium compositions as semiconductor materials ledto the development of certain metaphosphate compositions which aredisclosed and claimed in our copending application entitled, CeramicCompositions, Ser. No. 266,062 filed Mar. 18, 1963, now Patent No.3,278,317. This approach resulted in obtaining glass-es which could beproduced in relatively large melts and which nevertheless had thedesired electrical properties.

It has now been found that vanadium phosphate glass containing a majorportion of vanadium pentoxide can be treated according to the novelmethod disclosed herein in order to produce various degrees ofcrystallization. This crystallization is effective to produce arelatively large change in the specific resistivitiesof the materials.For example, a vanadium glass containing potassium metaphosphate wastreated by a method according to the present invention to thereby reduceits specific resistivity from about ohms per centimeter to 10 ohms percentimeter.

Briefly, the present invention contemplates heat treating vitreoussamples to produce varying amounts of crystallization to thereby producea relatively large change in the specific resistivity. This change inelectrical resistance is particularly dependent upon the thermal historybelow the liquidus temperature but above the transformation range of thematerial. The aforementioned thermal history relates to a heattreaatment which may be subsequent to the normal casting and annealingprocedures.

The invention will now be described in more detail in connection withthe accompanying drawings in which:

FIG. 1 is a graphical representation showing the change in resistivitywith respect to the change in vanadium oxide;

FIG. 2 is a graphical representation showing the rela- Patented July 16,1968 ice tionship between specific resistivity and temperature for avanadium oxide potassium metaphosphate glass;

FIG. 3 is a graphical representation showing the elfect on specificresistivity when the vanadium oxide potassium metaphosphate glass isheld at various temperatures for five hours; annealed and measured at 40C.;

FIG. 4 is a graphical representation showing the variation in specificresistivity when samples of vanadium metaphosphate glass are held at 310C. for various times, then are annealed and measured at 40 C. and,

FIG. 5 is a graphical representation showing the infrared transmissionof one sample of vanadium phosphate glass at various temperatures.

The novel treatment may be defined as promoting nucleation andsubsequently crystallization in a vitreous material, frequently calleddevitrification. It is presently preferred to treat the materials bysubjecting them to heat, i.e. to a temperature between the liquidustemperature and the transformation temperature for a period ofapproximately /2 hour.

The compositions set forth hereinafter show the raw batch analysis ofvarious vanadium phosphate glasses which have been used to illustratethe effect of treating such compositions by the novel method accordingto the present invention. As shown in the examples, the ceramicsemiconductors can be prepared from batch ingredients containing a majorportion (by weight) of vanadium pentoxide with a minor portion ofnumerous metal phosphates. Glass compositions containing vanadiumpentoxide in the amount of 60 to 84 weight percent in the batch havebeen shown to undergo devitrification during reheating. After castingthe molten glass, the ceramic material is heated in the temperaturerange between the transition temperature and the liquidus temperaturefor a period of time sufficient to alter the resistivity. Thesemiconductors are ordinarily used at ambient temperatures.

COMPOSITION A Ingredient Mole Wgt., Specific Percent Percent ResistivityV205 as. 22 75. o

NaPOs 30. 7s 25. 0 626K COMPOSITION B LiPO3 28.10 10.0 10K COMPOSITION oPbPOa 29.58 30.0 157K COMPOSITION D KPO; 33.48 25.0 239K COMPOSITION EEnrol 28.0 24.0 186K COMPOSITION F Gd(PO3)2 35.0 39K COMPOSITION GCd(PO3)2 30.0 27K COMPOSITION H Cd(PO3)2 25.0 10K COMPOSITION rVzO3Z3P2O5 40 870K COMPOSITION J COMPOSITION K V205 V20323P205 Thespecific resistiivties shown above relate to the specific resisitivitesof the vitreous glasses prior to subjecting the glasses tocrystallization.

The glasses set forth in the various examples may be prepared in variousways. For example, the ingredients in the powdered form are mixed andplaced in a platinum crucible. The crucible containing the mixture isplaced in an electric resistance furnace and the ingredients are meltedtherein at a temperature of approximately 900 C. Relatively small melt-swere made in this manner and were held at this temperature forapproximately 3-4 hours. Larger melts were also made at this sametemperature, however, were stirred according to conventional glassmaking techniques for approximately 4 hours. The smaller melts were castat approximately 900 C. on a plate having a temperature of approximately100 C. In the case of the larger melts the melt was cooled toapproximately 700 C, with continued stirring prior to casting on a plateof about 100 C. All types of the glass disclosed herein were annealed atapproximately 250 C.

Table I illustrates the effect of heat treating vanadium phosphatematerials at various temperatures and for various time intervals inaccordance with the novel method disclosed herein.

FIG. 1 is a typical curve showing the change in resistivity with respectto a corresponding change in composition. This curve was plotted forchanges in the rates of V in weight percent with respect to changes inBa(PO in weight persent. These changes are shown in tabular form inTable 11.

TABLE II Ingredient l ia iis e iit Iigiilsigfiy,

1, 700K as 193K 58: 8 240K 5313 93K 33:8 19K The specific resistivitiesshown were measured prior to subjecting the samples to the novel methodwhich is the subject of the present claims.

The relationship between specific resistivity and measuring temperatureis illustrated by the graphical representation shown in FIG. 2. Thegraphical data was obtained by measuring the specific resistivity ofglass samples taken from the melt identified as Composition D, i.e. acomposition containing weight percent V 0 and 25 weight percent KPO atvarious temperatures. The lower curve shows the temperature-resistivityrelation for the reheated material.

FIG. 3 shows the eifect of subjecting the glass taken from the samesample identified as Composition D to progressively higher temperaturesfor five hours. This shows that as a general rule there is a sharpreduction of resistivity as the temperatures are increased above thetransition range. The rate of change decreases as the temperatureapproaches the softening range.

The eifect of holding the sample 75 weight percent V 0 25 weight percentKPO i.e. Composition D at the same temperature i.e. a temperature whichis above the transformation range, for various periods of time is shownby the graphical representation in FIG. 4. This shows that the greatestdrop in resistivity occurs during the first half hour of treatment andappears to increase slightly when held at a longer period of time. Inthe case of the cadmium and lithium compounds the crystallized samplesgave higher resistances than their vitreous counterparts. In other casesthe resistances decrease as crystallization occurs.

The infra-red radiation transmission of the phosphate materials isgenerally similar to typical phosphate glasses. It has been notedhowever, as the vanadium content of these glasses is increased visibleradiation is absorbed and with a further increase in vanadium contentthis absorption extends into the near infrared region of the spectrum.The transmission characteristics of the glasses are shown by thegraphical representations in FIG. 5.

What is claimed is:

1. A method for manufacturing a ceramic semi-conductor materialcomprising heating a vanadium glass in the temperature range of about250 C. to 380 C. for at least one-half hour to produce crystallizationand change the resistivity of the ceramic material,

said vanadium glass consisting essentially of 60 to 84 weight percent V0 and 16 to 40 percent of a metal phosphate selected from the groupconsisting of barium metaphosphate, lead metaphosphate, lithiummetaphosphate, sodium metaphosphate, cadmium metaphosphate, potassiummetaphosphate and vanadium metaphosphate.

2. The method of claim 1 wherein the vanadium glass consists essentiallyof about 75 weight percent vanadium pentoxide and 25 percent potassiummetaphosphate, and wherein the glass is crystallized at about 310 C.

References Cited UNITED STATES PATENTS 3,278,317 10/1966 Blair et al.10647 OTHER REFERENCES Snell: Electrical Properties and Uses of Glass,Glass Industry, September 1962, page 484 only.

DONALL H. SYLVESTER, Primary Examiner.

G. R. MYERS, R. L. LINDSAY, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 3,393,()60 July 16 1968 Gerald E. Blair et a1.

It is certified that error appears in the above identified y correctedaspatent and that said Letters Patent are hereb shown below:

Column 4, line 45, "change" should read reduce line line 48, "40" shouldread 30 47 60 should read 7O weight lines 51 and 52, cancel "cadmiummetaphosphate Signed and sealed this 24th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer WILLIAM E. SCHUYLER, JR.

